I.

First, we have to consider the relative place which comparative

anatomy concedes to man in the 'natural system' of animals, for the

true value of our 'natural classification' is based upon its meaning

as a pedigree. All the minor and major groups of the system--the

classes, legions, orders, families, genera, and species--are only

different branches of the same pedigree. For man himself, his place

in the pedigree has been fixed since Lamarck,[4] in 1801, defined the

group of vertebrates. The most perfect[5] of these are the Mammalia;

and at the head of this class stands the order of Primates, in which

Linnæus, in 1735, united four 'genera'--Homo, Simia, Lemur, and

Vespertilio. If we exclude the last-named, the Chiroptera of modern

zoology, there remain three natural groups of Primates--the Lemures,

the Simiæ, and the Anthropi or Hominidæ. This is the classification of

the majority of zoologists; but if we compare man with the two chief

groups of monkeys--the Eastern monkeys (or Catarrhinæ) and the Western

or American monkeys (Platyrrhinæ)--there can be no doubt that the

former group is much more closely related to man than is the latter.

In the natural order of the Catarrhinæ we find united a long series

of lower and higher forms. The lowest, the Cynopitheci, appear still

closely related to the Platyrrhinæ and to the Lemures; while, on the

other hand, the tailless apes (Anthropomorphæ) approach man through

their higher organization. Hence one of our best authorities on the

Primates, Robert Hartmann,[6] proposed to subdivide the whole order of

the Simiæ into three groups: (1) Primarii, man together with the other

Anthropomorphæ, or tailless apes; (2) Simiæ, all the other monkeys; (3)

Prosimiæ, or Lemurs. This arrangement has received strong support from

the interesting discovery by Selenka that the peculiar placentation

of the human embryo is the same as in the great apes, and different

from that of all the other monkeys. Our choice between these different

classifications of Primates is best determined by the important thesis

of Huxley, in which, in 1863, he carried out a most careful and

critical comparison of all the anatomical gradations within this order.

In my opinion, this ingenious thesis--which I have called the Huxleyan

Law, or the 'Pithecometra-thesis of Huxley'--is of the utmost value.

It runs as follows: 'Thus, whatever system of organs be studied, the

comparison of their modifications in the ape-series leads to one and

the same result--that the structural differences which separate man

from the gorilla and the chimpanzee are not so great as those which

separate the gorilla from the lower apes.' If we accept the Huxleyan

law without prejudice, and apply it to the natural classification of

the Primates, we must concede that man's place is within the order

of the Simiæ. On examining this relation with care, and judging

with logical persistence, we may even go a step further. Instead of

the wider conception of 'Simiæ,' we must use the restricted term of

Catarrhinæ, and our Pithecometra-thesis has then to be formulated

as follows: _The comparative anatomy of all organs of the group of

Catarrhine Simiæ leads to the result that the morphological differences

between man and the great apes are not so great as are those between

the man-like apes and the lowest Catarrhinæ_. In fact, it is very

difficult to show why man should not be classed with the large apes in

the same zoological family. We all know a man from an ape; but it is

quite another thing to find differences which are absolute and not of

degree only. Speaking generally, we may say that man alone combines the

four following features: (1) Erect walk; (2) extremities differentiated

accordingly; (3) articulate speech; (4) higher reasoning power. Speech

and reason are obviously relative distinctions only--the direct result

of more brains and more brain-power, the so-called mental faculties.

The erect walk is not an absolutely distinguishing characteristic: the

large apes likewise walk on their feet only, supporting their bodies

by touching the ground with the backs of their hands--in fact, with

their knuckles--and this is a mode of progression very different from

that of the tailed monkeys, which walk upon the palms of their hands.

There are, however, two obvious differences in the development of the

muscles. In man alone the gastrocnemius and the soleus muscle are thick

enough to form the calf of the leg, and the glutæus maximus is enlarged

into the buttocks. A fourth glutæal muscle occurs occasionally in

man, while it is constantly present in apes as the so-called musculus

scansorius. Concerning the muscles of the whole body, we cannot do

better than quote Testut's summary: 'The mass of recorded observations

upon the muscular anomalies in man is so great, and the agreement of

many of these with the condition normal in apes is so marked, that the

gap which usually separates the muscular system of man from that of the

apes appears to be completely bridged over.'

[4] See note, p. 80.

[5] _Perfect_, in the sense of highest stage of evolution, may seem a

_petitio principii_. Leaving aside the consideration that no living

creature is absolutely perfect, in the sense that its organization

cannot become more efficient or proficient, we have here to deal with

relative perfection of the whole organization. A fish or a snake is in

its way more specialized than a mammal; but specialization does not

necessarily mean height of development: it generally means life in a

comparatively narrow groove. The acts of giving birth and nourishing

the young with the mother's milk is a much higher stage than the act

of laying eggs and letting them run their chance. The development of

a hairy coat goes along with heightened temperature of the blood,

subsequent greater independence of the surrounding temperature, and

increased steady activity of the brain and other nerve-centres. The

brain of the Mammalia, in its minute structure, is much more complex.

This rule applies to some of the principal sense organs, chiefly the

nose and the ear. The skeleton, not so much as a whole as in the

various bones and joints, is more neatly finished, and built up more

in conformity with 'scientific principles,' than is the case even with

birds, in spite of their marvellous specialization. The same is the

case with the vascular system, notably the heart and the veins, and

with the excretory organs. In all of these many imperfections, still

to be found in the other classes, have been corrected in Mammalia. The

Primates take an easy first by their hands, and among them the apes and

man himself by their brains.

[6] 'Die menschenähnlichen Affen und ihre Organisation im Vergleich zur

menschlichen.' 1883.

There are, for example, the muscles of the ear. In most people the

majority, or even all of them, are no longer movable at will, while in

the apes they are still in use. The important point, however, is that

these muscles are still present in man, although often in a reduced

condition. They are the following: (1) Musculus auricularis anterior

or attrahens auris, which is frequently much reduced and no longer

reaches the ear at all, being then absolutely useless; (2) Musculus

auricularis superior or attollens auris, more constant than the former;

(3) Musculus auricularis posterior or retrahens auris, likewise often

functional. Occasionally smaller slips differentiated from these

three muscles are present, and as so-called intrinsic muscles are

restricted to the ear itself; their function is, or was, that of

curling up or opening the external ear.

[Illustration: OUTLINES OF THE LEFT EAR OF--

1. _Lemur macaco_; 2. _Macacus rhesus_, the Rhesus monkey; 3.

Cercopithecus, a macaque; 4. human embryo of six months; 5. man, with

Darwin's point well retained: the dotted outline is that of the ear of

a baboon; 6. orang-utan (after G. Schwalbe):[7] ^x the original tip of

the ear; 7. human ear with the principal muscles.

[7] G. Schwalbe, 'In wiefern ist die menschliche Ohrmuschel ein

rudimentäres Organ?'--In what Respects is the Human Outer Ear a

Rudimentary Organ? (_Archiv f. Anatomie und Physiologie_, 1889).]

In connection with the ear, I may touch upon another interesting

and most suggestive little feature which is present in many

individuals--namely, 'Darwin's point.' This is the last remnant of the

original tip of the ear, before the outer, upper, and hinder rim became

doubled up or folded in. It is a feature quite useless, and absolutely

impossible of interpretation, excepting as the vestige of such previous

ancestral conditions as are normal in the monkeys.

In some cases the reduction of muscles has proceeded further in apes

than in man--for example, the muscles of the little toe. Another

instance is afforded by the coccyx or vestige of the tail; this is

still furnished with muscles which are now in man, as well as in

the apes, quite useless, and vary considerably with every sign of

degeneration, most so in the orang-utan.

Darwin has mentioned the frequent action of the 'snarling muscle,' by

which, in sneering, our upper canine teeth are exposed, like those of a

dog prepared to fight.

Monkeys and apes possess vocal sacs, especially large in the

orang-utan; survivals of them, although no longer used, persist in man

in the shape of a pair of small diverticula, the pouches of Morgagni,

between the true and the false vocal cords.

'In the native Australians, the dental formula appears least removed

from the hypothetical original type, for in it are still found complete

rows of splendid teeth, with powerfully-developed canines and molars,

the latter being either uniform, or even increasing in size, as we

proceed backwards, in such a way that the wisdom tooth is the largest

of the series. This is decidedly a pithecoid characteristic which is

always found in apes. The upper incisors of the Malay, apart from their

prognathous disposition, have occasionally a distinctly pithecoid

form, their anterior surface being convex, and their lingual surface

slightly concave. The ancestors of Europeans seem to have had the same

form of teeth, for the oldest existing fragments of skulls from the

Mammoth age (_e.g._, the jaws from La Naulette, in Belgium) reveal

tooth-forms which must be classed with those of the lowest races of

to-day.'[8]

[8] Wiedersheim, 'Der Bau des Menschen als Zeugniss für seine

Vergangenheit.' Freiburg, 1888. Translated: 'The Structure of Man an

Index to his Past History.' London, 1895.

Now we are able to apply this fundamental Pithecometra-thesis directly

to the classification of the Primates and to the phylogeny of man,

which is intimately connected with it, because in this order, as in

all the other groups of animals, the natural system is the clear

expression of true phylogenetic affinity. Four results follow from our

thesis: (1) The Primates, as the highest legion or order of mammals,

form one natural, monophyletic group. All the Lemures, Simiæ, and

Homines descend from one common ancestral form, from a hypothetical

'Archiprimas.' (2) The Lemures are the older and lower of the natural

groups of the Primates; they stand between the oldest Placentalia

(Prochoriata) and the true Simiæ. (3) All the Catarrhinæ, or Eastern

Simiæ, form one natural monophyletic group. Their hypothetical

common ancestor, the Archipithecus, may have descended directly or

indirectly from a branch of the Lemures. (4) Man is descended directly

from one series of extinct Catarrhine ancestors. The more recent

ancestors of this series were tailless anthropoids (similar to the

Anthropopithecus), with five sacral vertebræ. The more remote ancestors

were tailed Cercopitheci, with three or four sacral vertebræ.

These four theses possess, in my opinion, absolute certainty.

They are independent of all future anatomical, embryological, and

palæontological discoveries which may possibly throw more light upon

the details of our phyletic anthropogenesis.